An arrhythmia is a disturbance in the normal rate, rhythm or conduction of the heartbeat. A tachyarrhythmia is a condition in which an arrhythmia occurs at a high rate. Arrhythmias are classified broadly based on the chamber of the heart in which the arrhythmia originates. Such classification includes supraventricular or atrial tachyarrhythmia, ventricular tachyarrhythmia, or concomitant supraventricular and ventricular tachyarrhythmia.
A conventional implantable medical device (IMD) generally detects an atrial tachyarrhythmia by analyzing the rate of atrial depolarizations or the time interval between atrial depolarizations. A higher rate of atrial excitation generally indicates a shorter interval between depolarizations. When, for example, a patient's atria activate so frequently that the time between depolarizations is below a predetermined atrial tachycardia detection interval (ATDI), the IMD identifies the event as an atrial tachyarrhythmia.
Conventional therapies for atrial tachyarrhythmias include anti-tachycardia pacing (ATP), cardioversion or defibrillation. ATP involves the application of a train of high rate pulses to the heart to restore a normal rhythm. Cardioversion and defibrillation both involve the application of high-energy pulses to the heart to restore a normal rhythm.
A conventional IMD operates to terminate an episode of atrial tachyarrhythmia in response to a detected rate of atrial depolarizations, or equivalently, in response to a detected abnormal interval between depolarizations. When a conventional IMD detects that the median atrial activation interval is above the ATDI, for example, the IMD delivers a therapy in attempt to terminate the atrial tachyarrhythmia episode. In some instances, the IMD processor may erroneously indicate that the episode is terminated subsequent to the delivery of therapy when the episode of atrial tachyarrhythmia may not have been terminated, even if the median atrial activation interval is above the ATDI.